We also can disappear but we are alive and we are gaining bitcoins. I'm talking about the fact that the whole world is something temporary but if exists you have to use this.
This question should not be ask as in the first place nothing is permanent in this world so obviously bitcoin can disappear.
But, if we keep supporting bitcoin and do our job as members of the community to promote bitcoin, we can grow the community to a big family that will make the bitcoin economy stronger and might stay for long before it will disappear.
There is always a possibility that bitcoin will disappear since bitcoin is uncertain, but i agree with the man on my top, supporting bitcoin is the best way to make the life of bitcoin will go longer and make it stronger in the future.